Such droplet dispensing devices are also sometimes called aerosol generators, nebulizers and the like. They normally contain a nozzle body on a support part, in particular, a nozzle body of a liquid droplet spray device which dispenses a liquid substance as a liquid droplet spray or from the device through the nozzles of the nozzle body. They further consist of an actuator based on a vibrating element which generally causes the liquid to vibrate, to be accelerated and expelled as droplets. They further consist of elements such as liquid space, liquid feed and fluid interface to a reservoir, a reservoir as well as electrical connections between the vibrating element and a corresponding electronic circuitry. The elements may be contained in the aforementioned support part, in a further support part or they may be contained in a number of support parts. The support part or parts and elements need to be manufactured and assembled with the actuator and the vibrating element. The liquid may be for example an ambient fragrance, a perfume, an insecticide, a liquid pharmaceutical formulation, aqueous based liquids and flammable or combustible liquids.
Such nozzle bodies are sometimes called aperture plates, nozzle arrays, dosing aperture, orifice plate, vibratable membrane member, dosing aperture arrangement, aerosol generator and the like. The terms are hence to be understood as being interchangeable throughout the present document.
In fact such nozzle bodies and droplet spray devices are well known. For example see the document EP 1 129 741 in the name of the present Applicant. This document describes a liquid droplet spray device having a top substrate formed of a main body and of a nozzle body. The nozzle body contains a nozzle array of liquid droplet outlet means allowing a liquid substance contained in the liquid droplet spray device to exit the device, in this case as a spray of droplets. The nozzle body is conventionally formed of a nozzle array made out of silicon, a polymer, a resin such as SU-8, Nickel, a metal alloy, Parylen, Duroplast or any suitable material or combination of these and other materials that allows for a sufficiently precise and cost-effective manufacturing of the outlet nozzle array. Beyond well-known silicon, metal and SU-8 resin micro-machining methods the nozzle array could also be produced by methods using tools made with silicon micro-machining and other known replication methods like LIGA (Lithography-Galvano forming), hot embossing, UV printing, polymer and powder micro-injection moulding, micro-EDM and similar advanced 3D micro-machining methods and suitable combination of methods using photolithography and micro-structuring of resins, silicon, metal and plastic.
The documents U.S. Pat. No. 6,722,582 and EP 1 273 355 also in the name of the present applicant disclose such micro-machining methods.
The document U.S. Pat. No. 6,536,682 shows an actuator component for a piezo-electrically driven atomizer which features a vibrating diaphragm formed specifically in a semiconductor substrate on which the liquid is suitably fed and atomised according to the capillary wave theory, i.e. at an vibration frequency in excess of 2 MHz. The device uses one single large aperture since at these frequencies nozzles are not needed to create the aerosol, droplets are directly formed from the free surface of the liquid according to the capillary wave theory. No nozzles in principle means no opportunity of clogging, open aperture in principle means that the device can leak if not in a horizontal position or closed off. According to the disclosure the device is supplied with liquid from an excess pressure container. It appears that a semiconductor substrate would be an expensive material just to produce a membrane on which to join a piezoelectric element for providing ultrasonic vibration.
The document U.S. Pat. No. 7,066,398 discloses the manufacturing method of a particular aperture plate by means of an electrically conductive mandrel on which nonconductive islands have been formed from a photo-resistant material using a photolithography process. By placing the mandrel in a galvanic bath containing the desired material for the aperture plate, the material is deposited and grows on the conducting areas whereas the non-conductive islands will form the aperture openings according to their particular shapes. After one or more deposition steps, the aperture plate can then be released from the mandrel and shaped as desired.
The document U.S. Pat. No. 6,802,460, in the name of the present Applicant, shows another example of a nozzle body attached to a main body allowing for ejection of liquid from the device through the nozzle of the nozzle body.
The document PCT/EP2006/006059, also in the name of the present Applicant, shows such a droplet spray device including the nozzle body, the support parts and the actuator containing the vibrating element as well as a general way of assembling such a device.
Documents US 2004/0263567 and EP-A-1 604 701 also in the name of the present Applicant, show examples of various device configurations for which such a droplet spray device can be produced and needs to be assembled into in an efficient and cost-effective manner.
The complete disclosures of document PCT/EP2006/006059, and its corresponding U.S. patent application Ser. No. 12/095,695, are herein incorporated by reference. Likewise, U.S. Pat. No. 6,802,460, US 2004/0263567, U.S. Pat. No. 6,722,582, and EP 1 273 355 and U.S. Patent Application Publication No. US 2004/0124173 A1 (which corresponds to EP 1 273 355) are herein incorporated by reference. Also, EP 1 129 741 and its corresponding U.S. Pat. No. 6,196,219, and EP-A-1 604 701 and its corresponding U.S. Patent Application Publication No. US 2009/0084867 A1, are herein incorporated by reference.
As can be seen from the cited prior art documents, all of them approach mainly a particular aspect of the manufacturing of a particular component of the respective droplet spray devices, but fail to take a total device approach to the industrial production and assembly of components and device. In fact these devices, together with others fall into the category of Multi-Material-Electro-Mechanical Systems. Generally, the construction, the production and the assembly of such devices requires to dominate several main criteria or problems which additionally to attaining the lowest possible cost may present contradictory effects and conditions.
The effects and conditions firstly refer to the need to provide capillary feed or feed at very low pressures well below one mbar (100 Pa) or fractions thereof. Capillary feed for some liquids will refer to liquid channel, chamber and other fluid handling structures or features with dimensions of a few hundred microns to below 100 μm, often in the range of 10 to 50 μm, absolute evenness and smoothness of wetted surfaces and absence of dead spaces, corners and pockets in order to avoid even minute bubble traps. These bubbles, consisting of air surrounded by an ultra-thin film of the liquid, tend to block the capillary feed, hence the device functionality in a very effective manner.
The second problem is that leak-tightness needs to be guaranteed for a variety of liquids. Leak-tightness normally implies rigid body construction and assembly of its components and long-term resistance of the components to sometimes aggressive solvents.
The third problem is to assemble the actuator in a way which provides the most efficient use of the ultrasonic energy delivered by the vibrating element, namely a piezoelectric element.
A further problem is the aforementioned lowest possible production cost together with a minimum of assembly operations in simple, reliable assembly steps.
A further problem is represented by the need to disassemble the droplet spray device after one or several uses in order not to discard all parts after use, but to discard only one part and to keep the others for further use after cleaning for example or to disassemble some parts for cleaning them periodically and to reassemble them again for further use.
As can be understood by the person skilled in the art, these criteria can be highly contradictory in their requirements and effects. Also, as said before none of the prior art devices discloses on how to achieve these contradictory criteria in one device or a family of devices.
Other prior art devices have addressed in more detail some individual problem areas. For example, document U.S. Pat. No. 6,554,201 discloses a method for producing an aerosol generator comprising a vibratable element, a vibratable member and a support member. The vibratable member itself contains a plurality of apertures that are configured to produce liquid droplets when a liquid is applied to the rear surface of the vibratable member and the vibratable member is vibrated at ultrasonic frequencies by the vibratable element comprising an annular piezoelectric element. The document further discloses over-moulding the vibratable member and the vibratable element with the support member, all elements being essentially concentric. The document further discloses the introduction of an annular and concentric stiffening element such as a washer and different sizes materials for the stiffener to produce different flow rates. The document is silent about how the liquid is applied to the rear surface of the vibratable member and if and how leak-tightness and optimal fluidic behaviour can be achieved with this construction.
Document U.S. Pat. No. 6,732,944 discloses an aerosol generator having a vibrating element on a vibratable member with a front, a rear, a plurality of apertures traversing from rear to front, an outer periphery and a support element disposed about the outer periphery. The document further discloses an isolating structure coupled to the support element in order to vibrationally isolate the vibrating element from the support structure. The document discloses that metal arms, elastomeric bushings, plastic legs and the like and materials such as silicone, urethane, elastomers and metals can be used, but is in general silent about how this feature can be integrated into a final device providing leak-tightness, fluidic optimization and low cost integration.
Document U.S. Pat. No. 6,926,208 discloses a fluid injection device with an aperture plate having an oscillating surface with tapered apertures thereon and various relatively complex combinations of fluid supply to the oscillating surface. Again this document is in general silent about how this feature can be integrated into a final device providing leak-tightness, fluidic optimization and low cost integration.
The previously cited document U.S. Pat. No. 7,066,398 discloses how the aperture plate is coupled to a supporting member having a piezoelectric transducer coupled thereon and an interface to couple the resulting fluid injection device to other components of the device. But the document is again silent about how this feature can be integrated into a final device providing leak-tightness, fluidic optimisation and low cost integration.
Document WO 03/068413 discloses a liquid spray-head comprising a flexible member surrounding a liquid ejecting member and thus flexibly connecting the liquid ejecting member to the device housing.
WO 2005/097349 is an other document which discloses an alike device without disclosing integration into a final device providing leak-tightness, fluidic optimisation and low cost.
Document WO 2005/024967 discloses a piezo-actuator for miniaturized pumps which according to FIGS. 1 to 6 includes a weak point, item 6 and 9, which helps in this case to accommodate the bending, hence the pumping motion of the piezo-element and thus the efficient filling and emptying of the cavity containing the liquid.
Document WO 2004/031580 discloses a micropump using the same principle by providing a support ring to isolate the actuator from the housing as shown with item 4a in FIG. 3a and by FIGS. 3b to 3d of this document.
Document US 2005/0201870 discloses a dosing device for dispensing a medium into an environment. The document describes another liquid droplet spray device and specifically shows in FIG. 1 a dosing aperture arrangement 5 made of silicon which is introduced into an upper part 3, also called wall portion, and secured with an adhesive connection 14 as disclosed in some of the previously cited documents. This document states in particular, that the specific production process for integration of the dosing aperture arrangement into the upper part can be chosen independently from the other portions of the device and that the process can be specially suitable for the dosing aperture arrangement. The document also discloses the provision of an elasticity zone on a second wall portion on which the vibration means is provided. The elasticity zone is laid out as a circular groove and provided to avoid at least substantially reduce unwanted transmission of oscillation to other parts of the device in a similar fashion as previously cited documents. Nevertheless and obviously the wall portion is later assembled in direct contact and rigidly into the other housing parts via a leak-tight, cohesive connection between parts and by means of adhesive bonding, ultrasound or laser welding. (See FIGS. 1, 2 and 4 of the document). However, the ultrasonic oscillation being represented by essentially planar ultrasound waves, the ultrasound energy will obviously nevertheless be transmitted to all connected parts via this rigid connection between parts, even if the rigidity is provided by a form-fit arrangement. The document further discloses a combination of circular and meandering channel to supply the liquid to the dosing space under the dosing aperture which in this case is a nozzle plate. The document clearly states that the circular and annular channel is of a substantially larger volume than the dosing space which has a height of approximately 50 μm. It is therefore obvious that the channel height is substantially bigger than the dosing chamber. This would imply that the channel is used mainly for priming and dosage storage reasons but would not retain the liquid close to and in fluidic contact with the dosing space once the device is in function. The document further mentions over-moulding of the aperture arrangement and of the vibration means and multi-component injection moulding.
Document EP 1 602 414 describes an ultrasonic atomizer utilizing surface acoustic waves. The atomizer comprises an oscillator generating surface acoustic waves, and a perforated porous thin plate arranged on an oscillating surface of the oscillator with a small clearance. Liquid is aspirated into the small clearance part between the oscillator and the porous thin plate by vibration by the surface acoustic waves or by capillarity. Vibration of the surface acoustic waves is transmitted to the porous thin plate through the liquid in the small clearance part, and a small quantity of liquid penetrates into the perforations, i.e. the outlet nozzles of this thin plate and is atomized by the vibration and sprayed to the exterior.
As will be explained later, Applicant has found that, contrary to what is stated in previously cited documents, the aperture arrangement indeed needs to be machined specifically to conform to an industrial production environment, specifically an injection moulding process and also to the specific functionalities of the devices, like chemical resistance to various liquids, fluidic optimisation, leak-tightness and the like.
Applicant has found that neither the circular groove elasticity zone nor a weak point nor multi-component injection moulding are necessary to provide an efficient, leak-tight, fluidically optimised and cost-effective device and that capillary feeding methods need to be innovated.
If channels are used for system priming and dose storage then clearly different designs for capillary feed need to be invented in order to maintain the liquid feed to the chamber or even to avoid flow back. To guarantee dimensions smaller than or substantially equal to 50 μm with reasonable tolerances using a filter membrane disk as disclosed in previously cited documents is another problem.
Applicant has found that for some liquids with a viscosity of for example approximately 3 cps (centipoises) a height of 50 μm is an upper limit for capillary flow and retention, meaning avoiding flow-back due to inclination, device handling and the like. Applicant has also found that under certain conditions and specifically with constructions where the channel height is larger than the dosing space height, maintaining the chamber filled under all conditions is highly unreliable and subject to rupture of the liquid column.
It is, therefore, an object of the present invention to provide an innovative droplet spray device and an innovative production and assembly method for such a device that overcomes the inconveniences presented by the prior art documents.